Gas test on old fire

Yes this is true. They will carry out a flue flow test to ensure 1. The flue is in sound condition with no escapes and 2. all the products of combustion are correctly exiting the building via the chimney. They will also carry out a spillage test to ensure none of the products of combustion are “spilling” into the property from the gas appliance. Both of these tests need to be passed to deem your appliance as safe to use.

That is correct.

There are two important tests gas engineers carry out to your flue way/chimney serving your gas appliance the first is a Flue flow test to ensure that all products of combustion escape to atmosphere and the second is a Spillage test to ensure the integrity of the flue way/chimney that no products of combustion are escaping in to your loft due to poor brickwork mortar that has eroded or fallen away space for example within your roof space/loft. But why do you ask this question have you any concerns?

Yes, they will test the "pull-on the chimney this is called a flue flow test, if this is satisfactory then the appliance itself is tested whilst using the same chimney

Yes, If it passes all well and good.If it fails the flue test or a spill test the whole thing is shut down.